Burner apparatus



Sept' 13 1960 l H. w. scHRAMM ETALA 2,952,307

BURNER APEARATUS Filed oct. 26,1955

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nited States Patent() BURNER APPARATUS Henry W. Schramm and ChesterCipriani, Toledo, Ohio, assignors, by mesne assignments, to Midland-RossCorporation, Cleveland, Ohio, a corporation of Ohio Filed oct. 26, 195s,ser. No. 542,9 2s -2 claims. (cl. rss- 7) This invention pertains toburning of combustible fuel and has particular application to apparatusfor'burning fuel with which a large temperature variation may beattained.

There are a large number of applications for such apparatus. A typicalexample of this is a batch type furnace in which Work is to be hardenedand then drawn. The first operation may require a furnace temperature ofl700 F. and the latter, a temperature of' 700 F. Unless the singlefurnace has burner'equipment capable of properly operating at andmaintaining both of. these temperatures, two separate furnaces must beemployed.

A large temperature Variation has been previously attempted with avariety of apparatus. For instance, two or more separately controllablesets of burners have been employed. All sets of burners would be usedwhen high temperatures were desired and one or more setswould then beturned off when lower temperatures were to be maintained. This system,although relatively inexible, worked reasonably well but resulted in ahigher first cost for such furnace installations due to the extra numberof burners necessary. Theextra burners also resultin extra controls,extra fuel, additional piping, and additional space. Also, these burnersdid not create comparatively large temperature ranges in the furnacechamber even when several sets of burners were employed.

As an alternate to this system, a single set of larger combustibleair-gas mixture would be fed directly into the furnace chamber with anexplosion hazard resulting. This is not a danger at higher temperatures,labove 1400" F., since the tunnel walls of the burner will bemaintained, Idue to heat from the furnace chamber, at temperatures thatwill ignite the air-gas mixture on contact if the pilot is extinguished.

A third means of attaining a large temperature range in a furnacechamber was by variation of the firing rate of the burners in place ofoperating them in an on-oif manner. However, such burners must have avery large range of turndown to fire properly at the Very low tiringrates required for low furnace temperatures. Burners are designed totire at certain capacities, however, and will only operate properlywithin certain variations from this capacity, most burners having aturndown range of less than 4 to l. To produce a temperature range in afurnace of, for example 700 F. to 1700" F., a much larger range ofturndown is required.

In such cases, at the required very low rates of firing, the volume ofair and gas passing through the burner nozzle is reduced and thevelocity thereof is likewise decreased. However, the rate of flamepropagation will be constant with the result that, as the velocity ofthe air-gas mixture is decreased, the flame moves back through thenozzle. The velocity of flowback of the nozzle is, of course, less thanthat through the nozzle burners has been used in place of the above andare operated at their full firing rate at higher temperatures and in anon-ol manner at lower temperatures. Howeverg such burners are incapableof maintaining a steady temperature particularly below 1000 F. whencontrolled by a thermocouple and temperature control instrument. v

With this system, the burners `are turned oi when the temperature of thechamber slightly exceeds the control tempera-ture and are likewiseturned on when the temperature falls slightly below this controltemperature. However, the heating elect from the burners continues, atthese lower temperatures, to raise the temperature of the chamber evenafter the burners are shut olf with the result that the controltemperature is overridden and large temperature variations occur-thelower the temperature desired to be maintained, the larger the variationin temperature actually attained. During the period the burners are notfiring temperature differences within the chamber also result due tolack of circulation. -This will be more fully discussed subsequently.Furthermore,

with the result that the ilame, once having penetrated back through thenozzle, spreads quickly through the remaining air-gas mixture up to thepoint where the air and gas are combined. This explosion, or backring,may damage the apparatus, particularly if there is a large volume of theair-gas` mixture. Even without damage occurring, there is dangerinvolved since the explosion generally extinguishes the ame with theresult that the subsequent unignited mixture is emitted intothe furnacechamber.

Topovercome this, a burner may be supplied mixture through separate airand gas conduits whose outlets lie behind, and adjacent to, the nozzle.Any backring occurring here, then, merely extends to this point ofmixing with very little ignitable volume involved. A small backiringoccurring here, however, is still suicient to extinguish the flame whichagain results in the mixture being fed, unignited, into the furnacechamber. If backring will not extinguish the flame, an unstable llamefront may nevertheless occur thatcauses ineiiicient combustion andgenerally unsatisfactory operation of the burner. i Furthermore,particularly in burners of this nozzle mixing type, the air-gas mixtureis very diicult to proportion at very low tiring rates. Thus the correctstoichiometric mixture to give complete combustionjfor these burnersgenerally rely on pilots for ignition when turned on, and should thepilots be extinguished, the

In View of the aforementioned difliculties and manyl others, a burner`and method ofnoperation have beendeveloped that will operate effectivelyat full rates and Very low rates of liring with none of these problems.Furthermore, this burner is capable of producing a temperattire range ina furnace chamber of 400 to 2400 F. c I

For further consideration of what is novel and our in,-

Patented Sept. 13, 1960,

Vention, reference is made to the accompanying drawing, subsequentspecification, and claims.

In the drawing:

Figure 1 is a partially sectional end view of apparatus embodying ourinvention, and

Figure 2 is a side View shown partially in section as taken on line 2-2of Figure l.

The burner of Figure 2 comprises a tunnel block 11 and a holder 12attached to burner body 13. Tunnel block 11 is of refractory compositionand square configuration with a cylindrical tunnel chamber 14 extendinglongitudinally therethrough. The portion nearer the holder 12 is offsetto accommodate the holder which is generally made of cast steel and isadapted to be installed in a furnace wall and fastened to the outercasing thereof by means of bolts through bolt holes 15. Burner body 13is attached to holder 12 by means of bolts 16 extending through boltholes 17 land 18, located in body 13 and holder 12 respectively, and sopositioned that the body is properly aligned with respect to cylindricalchamber 14.

Burner body 13 has cast portions 20` and 21 united by bolts 22 extendingthrough bolt holes 23 and into tapped holes 24. This forms a cylindricalchamber 25 and a sharply tapered chamber 26 that tapers toward tunnelchamber 14. It also forms a smaller cylindrical chamber 27 that extendsslightly into tunnel chamber 14 and an air inlet passage 28 which tapersoutwardly from chamber 25. Air volume to this inlet is controlled byoriiice plate 29.

Cast portion, or rear wall, 20` has -a fuel port 30` drilled through itin `axial alignment with chamber 25, tapered chamber 26, small chamber27, and tunnel chamber 14. A fuel nozzle 31 is axially aligned with thisport 30 and threaded thereinto 4by means of fitting 32. A frustoconicalchamber 33 is formed around nozzle 31 by wall 34 which is integrallyconnected with portion 20. Wall 34 has four equally spaced yair ports 39drilled therein. In addition, it is suitably lthreaded yat its outerportion to receive tube 35 which is axially aligned with nozzle 31 andextends into tunnel chamber 14 past small chamber 27.

Fuel port 30 is supplied fuel through pipe nipple 36, T 37, and pipe 38which lead to a source of fuel (not shown). A Valve 40 is disposed inpipe 38 to control fuel flow therethrough; it is anelectrically-operated, motor-driven valve in the preferred form ofapplication. T 37 contains a plug 41 at its unused outlet which isperiodically removed and a brush or other suitable cleaning means isextended thereinto to clean port 30 and nozzle 31 in which carbon andimpurities in the fuel may gradually -be deposited.

Three tapped holes 42, 42a, and 42h are provided in portion 20. The axesof these holes intersect the superimposed axes of port 30, nozzle 31,tube 35, and the various chambers at some point within tube 35. Acommercially available flame rod safety device may be placed in one ofthese holes to shut olf a valve upstream of valve 40 should the flame intube 35 become extinguished. A sight glass may be installed in thesecond hole to permit limited observation of the internal operation. Inthe third hole, an ignition means may be placed to initially light thefuel-air mixture.

A movable air vane 43, which is somewhat similar to one in a PatentNumber 1,943,590 to Carroll Cone, may be placed at the entrance of airinlet passage 28 into chamber 25, and directs the air in a tangential orradial direction into chamber 25. The vane consists of a metal sheet 44rotatably attached to `a pin 45 which is horizontally disposed inchamber 25, parallel to the axis thereof, yand secured -at its ends toportions 20 and 21. A threaded shank 46, having a knurled head 47,extends through a tapped hole 48 in portion 21 and is rotatably securedto Vane 44.

When an electrically-operated, motordriven valve 40 is employed in fuelpipe 38, it is controlled by a temperature controller 50` through line51. This controller 50 is responsive to temperature in furnace chamber52 by a thermocouple or temperature bulb 53 which extends through thefurnace wall as represented by dotted line 54.

In operation, air is supplied through inlet 28 with the majority flowingthrough tapered chamber 26, small chamber 27, and into tunnel chamber14. A smaller portion of this air enters air ports 39 to subsequentlymix with a portion of the fuel emitting from nozzle 31. The Iairentering ports 39 is sucient to create a combustible mixture with aportion of the aforementioned fuel when ignited. This burning mixture,along with the raw fuel, passes out of tube 35 where the unignited fuelmixes with the additional air, forms a combustible mixture, and isignited by the former burning mixture. When the burner is firing at itsfull capacity, orifice plate 29 is sized to allow entry of sufficientair .to form -a stoichiometric mixture with the fuel that permitscomplete combustion with no residual air resulting. This is thepreferred method of operation with air being turned on and olf by avalve upstream of the orice. The burner will thus oper-ate atstoichiometric proportions of fuel and air as long as it is operating atcapacity which will be maintained until the temperature of the furnacechamber reaches that desired. At this point, temperature controller 50will tend to close valve 40. An excessive `amount of air will then besupplied to the burner for the amount of fuel input and this excess willincrease for lower furnace temperatures where the fuel input is furtherdecreased. However, the burner will still operate efficiently and with apositive, stable ame for any air-fuel ratio that may be created. This isachieved for two principal reasons: The llame emitting from tube 35forms Ia constant point for ignition of the air and unburned fuel thatinitially mix at this point; this helps assure a stable flame front.Secondly, the air and fuel emerging from separate points tend to mixslowly enough to prevent excesive dilution of the fuel in the air beforeignition can occur and thus form an unignitable mixture. This is trueregardless of the amount of excess air encountered since, upon emissionfrom tube 35, the combination fuel and burning mixture immediately beginto m-ix With the air, with additional combustion occurring constantly.Such mixing prohibits excessive dilution since this additional burningconstantly occurs as soon as a portion of the unburned fuel mixes withsucient air to support combustion. Furthermore, .the raw fuel in tube 35is heated by the ignited portion of fuel and air therein. This heatedfuel then tends to expand as it emits from the relatively conned volumedefined by tube 35. The expansion hastens mixing of the fuel and airsuiciently to prevent the possibility of excessive air from lowering thetempera-ture of the air-fuel mixture to the point where the llame willbe extinguished.

When very low temperatures of approximately 400 to 600 F. are desired in`the furnace, the fuel supplied will be decreased to a point where allthe fuel is burned with the air entering ports 39 and no burning occursin tunnel chamber 14. Again, there is a stable flame produced withefcient burning. This occurs because the air entering ports 39 isdirected toward the rear of chamber 33 `to prevent -any possibility ofits velocity blowing off the flame. The -air will thus properly supportcornbustion for even the smallest amount of fuel emitting from nozzle31, and, of course, for higher rates of fuel ow the uucombusted fuel iscombusted with the air emitting from small chamber 27. Therefore, it maybe seen that eicient combustion and a stable, positive flame occurs forany rate of fuel flow.

The use of excess air at all but full firing rates has severaladvantages, particularly for lower furnace temperatures. This air, uponleaving chamber 27, mixes with the products of combustion and thusdecreases their temperature which permits an even lower furnacetempei-rature to be attained. Of more importance, however,

is the fact that this air circulates the heat through the furnacechamber and thus aifords greater heat distribution than otherwisepossible. If the burner, at low rates of firing, Were to operate with noexcess air, this heat, due to lack of volume for circulation, would tendto be limited to -a relatively hot area adjacent the burner. At fullrates of tiring, the volume of products of combustion are large enoughto supply the necessary circulation -but for lesser firing rates theexcess air must provide this. Furthermore, vthe-use of excess airpermits the furnace pressure to be maintained above ambient whereasnormally with low ring rates, the volume of combusted products isinsufficient to effectively provide such pressure. Without this positivefurnace pressure, relatively cool, ambient air tends to enter throughvarious furnace openings such las at charge and .discharge ports. This,of course, develops areas of cooler temperatures which further varytemperature distribution.

Additional versatility is provided in our invention due to vane 43.Sheet 44 of the vane may be moved from the position shown in Figure 1 toa middle position in inlet passage 28. In the former position, all theair enters chamber 26 tangentially and is thereby spun around tube 35and Wall 34. 'I'his air, still spinning, is pushed out through taperedchamber 26 and small chamber 27 into tunnel chamber 14 where it mixeswith unburned fuel from tube 35. The total mixture of fuel, air, andcombusted products is thereby spun and, as it emits from the contines oftunnel chamber 14, expands both forward and radially, the exactdirection depending on the degree of spin imparted to the mixture. Thisflame emitting from tunnel chamber 14 thus appears as a cone, the apex`angle of which varies With the spin as heretofore mentioned. Such `aflame conliguration is useful in a variety of applications las, forinstance, where work being heat treated is situated `in front of theburner and it is desirable for the burner flame not to impinge thiswork.

For lower firing rates, of course, the flame will not extend beyond thechamber 14, but the hot mixture of combusted products and air will do soand spinning in this case helps create greater heat distribution.

In the latter position of sheet 44, `air enters chamber 25 substantiallyequally on 4both sides of tube 35. Tendency to spin iis thuscounter-acted and the air moves through tapered chamber 26, smallchamber 27, and tunnel chamber 14 in substantially straight flow. Thisair mixes more slowly with the fuel and products of combustion from tube35 and results in a somewhat longer llame. Furthermore, this flame tendsto emit straight outward from tunnel chamber 14 in an axial directionwhich results in a long, directional flame that likewise has variousapplications, as where the burners are placed below or above the workbeing heat treated.

Vane 43 is adjusted by screwing threaded shank 46 in or out by turningknurled knob 47. Once this vane is adjusted, it is seldom necessary tomove it unless the physical conditions under which the burner isoperated vary.

Typical data showing the range of turndown and the variation in flamelength when using oil for fuel are presented below:

Air Input, OilInEut, Air Pres- Oil Pres- Flame c.f.h. g.p. sure, Oz.sure,p.s.i. Air Direction Length,

S.I. Feet 10. 60 9. 8 75. 0 Straight.-." 9 10. 60 9. 8 75. O Spinning 68. 48 9. 8 48. 0 Straight 9 8.48 9.8 48. 4 6. 35 9. 8 27. 5 8 6. 35 9. 827. 5 3 4. 24 9. 8 13.0 4 4. 24 9. 8 13. 0 2 2. 12 9. 8 3. 4 Straight 12.12 9.8 3. 4 Spinning--- 0. 8 0. 706 9. 8 0. 42 Straight.- (l) 0. 7069. 8 0. 42 Spinning-.- (1) 1 Flame within tunnel.

- aresasoi For gas fuel, the burner is evenrmore eifective as evident inthe 'following representative data:

. Gas Pres- .Air Input, Gas Air Pressure, Flame c.i.h. Input, sure Oz.Inches of Air Direction Length,

c fn si. Water Feet 1500 11. 0 0. 6 Straight... 8. 5 1500 11. 0 0. 6Spinning--.. 3 1200 11. 0 0. 4 Straight-.-" 8 1200 11.0 0. 4 Spinning 2900 11. 0 0. 3 Straight. 4 900 11. 0 0. 3 2 600 11.0 0.15 3 600 11. 0 0.15 Spinning 1. 5 300 1l. 0 0. 08 Straight 2 300 11. 0 0. 08 Spinnjng 111. 0 0.05 Straight---. (4)

25 11. 0 (l) Spinning- (3) Inches of Water 3000.- 300 5. 0 (4)Straight.-. 3 300 5. 0 (4) Spinning- 8 250 5. 0 (4) Straight-.." 2. 5250 5.0 (4) Spinning 7" 200 5.0 (4) Straight 2. 5 200 5. 0 (4) Spinning6 5.0 (4) Straight--." 2 150 5. O (4) Spinning 6" 100 6. 0 (4) Straight.l. 5 100 5.0 (4) Spinning 6 50 5. O (4) Straight- 6 50 5. 0 (4) Spinning4" 5 5. 0 (4) Straight (2) 5 5. 0 (4) Spinning.- (2) 1 Not measurable.

2 Flame within tunnel.

a Flame within inner tube. 4 Not measured.

It may be seen then, that the versatility of our burner is extended notonly over a large range ofy temperatures, but also over a variety ofilame lengths and flame shapes, the latter ranging from linear toconical.

It may be noted here that whether air enters chamber 25 radially ortangentially, the volume of air entering ports 39 is not substantiallyvaried. This is true since, regardless of the :mode of air entry,pressure in chamber 25 remains relatively constant due to therestriction afforded by tapered chamber 26 and small chamber 27, andthus forces a relatively constant volume through ports 39.

The foregoing disclosure is the best mode known to the inventors ofcarrying out this invention, the scope of which is limited only by theappended claims.

We claim:

1. Burner apparatus for burning fuel at a wide range of inputs in afurnace chamber comprising: a refractory lblock containing a cylindricaltunnel chamber extending longitudinally therethrough; a holder lforattaching said block to a wall of said furnace; iirst Wall meansattached to said holder and forming a small cylindrical chamberextending into said tunnel chamber, a tapered chamber With the smallerend thereof meeting the end of the smaller cylindrical chamber away fromsaid tunnel chamber, and a larger cylindrical chamber with one endthereof meeting the larger end of said tapered chamber, the threechambers being substantially axially aligned with said tunnel chamber;rear wall means forming a closed end for said large cylindrical chamberat the other end thereof; an air inlet to said large cylindrical chamberlocated at one side thereof; nozzle means extending into said largecylindrical chamber, in substantially axial alignment with, and directedtoward, said tunnel chamber; pipe means connecting a source of fuel tosaid nozzle means; and second wall means forming a cylindricalcombustion chamber extending from said rear wall means, around saidnozzle means, and into said tunnel chamber, said combustion chamberbeing in substantially axial alignment with said tunnel chamber andforming a series of equally spaced air ports for emitting air from saidlarge cylindrical chamber substantially radially to said combustionchamber at a point upstream of the outlet of said nozzle means, and saidsmall cylindrical chamber forming a restricted annular passage with saidsecond wall means for the passage of air therethrough from said airinlet and said large cylindrical combustion chamber.

2. Apparatus according to claim 1 characterized by an electricallyoperated valve in said pipe means, and control means responsive to thetemperature of the furnace chamber for operating said valve to vary therate of gas ow therethrough, said air inlet containing a constant re- 10striction whereby the ow of air therethrough will remain unchanged.

References Cited in the le of this patent UNITED STATES PATENTS KempOct. 13, 1903 Cone Apr. 3, 1934 Bloom May 17, 1938 Naab et al. July 25,1939 Maienshein Jan. 10, 1950 FOREIGN PATENTS Great Britain Nov. 24,1937

